Quitting is uncommon. The expectation is that a pope, once elected, will serve until he dies.

After resigning, Benedict will have to relinquish the emblems of his office. That includes his papal ring, which will be destroyed with a special silver hammer; his red shoes that symbolize the blood of martyrs; and his Swiss Guard, one of whom can be seen polishing ceremonial armor in the picture above, taken around 1938.

The Swiss Guard started working for the Roman Catholic Church in 1506. Its origins were a group of 150 mercenaries brought in by Pope Julius II to safeguard Rome against sacking. Still trained in combat today, the Swiss Guard's job is to protect the pope. Members wear a type of helmet, called a morion, seen on the shelf above this guardsman's head.

Though it has been employed by popes for over half a millennium, this is the first resignation the papal army will have seen. The last pope to resign, Gregory XII, did so almost a hundred years before the Swiss Guard first entered the Vatican.

In 1415, three popes claimed rule at the same time, so Gregory XII took off the mitre and bowed out in hopes of reconciling the schism.

Three other Benedicts also had unexpected ends to their papal reigns. Benedict V was forced by Emperor Otto III to admit he wasn't a true pope just a year after he'd been given the office in 964 then had the papal staff broken over his head.

In 974 Benedict the VI was tossed into prison and strangled. Benedict IX wore the mitre three different times in the 1030s and 1040s: He stepped down once, sold the position for profit and the promise of a wife the second time, and was pushed out during his third stint as head of the church.

Other popes had even more ignominious ends.

Pope Formusus died in 896, several years after being first excommunicated and then pardoned. But his corpse was exhumed a year later, tried by the new pope, and deemed unworthy of being considered a pontiff. Instead of reburying Formosus, the new leader, Stephen VI, invalidated his predecessor's papal edicts, had the three fingers he used in consecrations torn off, then chucked his body in the Tiber River.

Editor's note: This is part of a series of pieces that looks at the news through the lens of the National Geographic photo archives.